The present invention relates to a method of producing saturated vapor of solid metal organic compounds in the metal organic chemical vapor deposition (MO-CVD) method of semiconductor metal organic compounds.
Today, as a method capable of mass-producing semiconductor laser etc. in good efficiency upon manufacturing them, the MO-CVD method using metal organic compounds is well-known. Also, the MO-CVD method is applied to the manufacture of oxide type superconducting thin film.
The MO-CVD method is a method wherein the metal organic compound is contacted with the carrier gas such as inert gas, hydrogen gas or the like, they are fed onto a wafer being under high temperature as a saturated vapor of metal organic compound and are allowed to react with raw material gas on the wafer to deposit a thin film of single crystal of compound produced through said reaction. In more detail, this is a method to deposit a thin film of single crystal of, for example, GaAs by allowing (CH.sub.3).sub.3 Ga to react with AsH.sub.3 gas on the wafer being under high temperature through following reaction equation. ##STR1## In the MO-CVD method, the metal organic compound charged in a cylinder is carried with carrier gas into a reaction furnace to deposit the crystal.
As a prior art, there is a proposal of cylinder for MO-CVD method disclosed in Japanese Unexamined Patent Publication No. Sho 63-11598. Here, as shown in FIG. 3, a disperser (filter) (4) is attached to the lower part of carrier gas-introducing pipe (3) being connected to an inlet pipe (1) of carrier gas and passing the center axis of a cylinder (2), the lower part (2-1) of the cylinder (2) is made to be a narrow diameter part, the inner diameter being narrower compared with the upper part (2-2) of the cylinder, and yet, a tilting part (2-3) is provided onto said narrow diameter part so that the carrier gas introduced from the introducing pipe (3) to the bottom of cylinder (2) via the disperser (4) is saturated with the vapor of metal organic compound during rising the inside of cylinder (2) charged with metal organic compound and discharged from a discharging port (5) to outside of cylinder. According to said proposal, the effect was seen at the time of, in particular, solid metal organic compound, but it proved to be still insufficient.
In said proposal, trimethyl indium (TMIn) is used as a metal organic compound and the supply level of TMIn is determined by discontinuously varying the charge level within a range of 5 to 50 g.
With this method, the charge state of TMIn before starting of supply test is very good for each level of TMIn and, since the flow rate of carrier gas is not so high and yet the time is relatively short being 3 hours, the charge state of TMIn after finishing of supply test hardly changes as the examples in said proposal show. Thereby, it is understood that the contact of TMIn with carrier gas is sufficient to easily reach the saturation resulting in a constant value of supply level.
However, when conducting the supply test adapted to the practical use method, i.e. when charging a fixed quantity of TMIn in the cylinder and flowing the carrier gas continuously for a long period of time, such a drawback has become evident that TMIn around the filter becomes hollow with the lapse of time producing flow paths of gas and the contact of TMIn with carrier gas becomes insufficient gradually resulting in a gradual decrease in the supply level and more difficult composition control of thin film of single crystal, though the change of charge state is hardly seen during a relatively short time as described above.
There, as a result of extensive investigations for further improvement, the inventors have found that, by providing an introducing port and a discharging port of carrier gas respectively to the cylinder and by feeding the carrier gas from introducing port into cylinder and discharging it from discharging port after the solid metal organic compound and the packing material are charged in the cylinder, into which a tube directly connected to either of those is inserted, very good results can be obtained even when the flow rate of carrier gas is high, leading to the completion of the invention.